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TypeScript Object Types

Describe the shape of objects.

✍️ 3 exercises + code challenge in this lesson
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Object types list each property and its type:

const car: { brand: string; year: number } = { brand: "Toyota", year: 2020 };

  • Optional property: color?: string
  • Read-only property: readonly id: number
  • Index signature for dynamic keys: { [key: string]: number }

Key Takeaways: TypeScript Object Types

Mastering TypeScript Object Types helps you write clean and reliable TypeScript code. Follow standard conventions, test edge cases, and keep logic simple. Try running the code example below and complete the exercises to build confidence.

TypeScript Object Types Code Example

TypeScript 
const car: { brand: string; year: number; color?: string } = {
  brand: "Toyota",
  year: 2020,
};

const stock: { [item: string]: number } = { Laptop: 12, Mouse: 150 };

console.log(car.brand, car.color ?? "no colour", stock.Mouse);
Output
Toyota no colour 150
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TypeScript Object Types Practice Exercises

Check what you learned in “TypeScript Object Types”.

/ 3 solved
Fill in the blank

Make the color property optional.

let car: { brand: string; color: string };
✓ Correct! Not quite. Try again.
Multiple choice

Which modifier prevents a property from being changed?

✓ Correct! Not quite. Try again.
Code challenge

Create book: { title: string; pages: number } = { title: "Clean Code", pages: 464 } and log book.title.

Write the code in the live editor. Your answer is checked automatically.

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TypeScript Arrays & Tuples
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TypeScript Type Aliases & Interfaces

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